1. Field of the Invention
This invention relates to disc-type valves used in the flow lines for fluid material to commence or halt the flow of such materials.
2. Description of the Prior Art
Disc-type valves are heretofore known have several problems. In disc-type valves, such as the known three-lever valves, the movement of the disc is such that it begins to pivot almost immediately as force is applied through the lever linkage. This pivotal motion causes the disc to slide across the surface of the valve seat in an abrasive fashion resulting in a scratched and abraded valve seat. Once the valve seat loses it original smooth finish, the ability of the valve to halt the flow of fluids is significantly reduced.
Due to the pressure differential encountered in closing the disc of a disc-type three lever valve, there exists in known valves of this type, a leakage problem caused by the force of flowing material through the valve, preventing the disc from fully seating itself against the valve seat.
All of the known butterfly valves encounter fluctuations in the rate and direction of flow of materials through them. In addition, various impurities of a physical quality different from that of the intended material, flow through the valve. The result is a tendency to cause the valve disc to flutter about its pivotal axis. Such flutter augments the fluctuation of flow and can cause the valve to partially close at an inopportune time.
In accordance with this invention, there is provided control of the motion of the valve disc such (a) that it is positively pulled away from the valve seat before it is pivoted, thus eliminating the sliding motion of the disc across the seat; (b) that it is closed through a positive means which insures full contact of the valve disc periphery against the valve seat upon closure of the valve; and (c) that it is held immobile in its open position despite the flow of fluid past the disc.